This invention generally relates to thermoplastics and articles formed therefrom. More particularly, the invention relates to a blend material prepared from a macrocyclic polyester oligomer and a polymerization catalyst, and processes of using the same.
Linear polyesters such as poly(alkylene terephthalate) are generally known and commercially available where the alkylene typically has 2 to 8 carbon atoms. They have many valuable characteristics including strength, toughness, high gloss and solvent resistance. Linear polyesters are conventionally prepared by the reaction of a diol with a dicarboxylic acid or its functional derivative, typically a diacid halide or ester. Linear polyesters may be fabricated into articles of manufacture by a number of known techniques including extrusion, compression molding, and injection molding.
Recently, macrocyclic polyester oligomers were developed which have unique properties that make them attractive as matrices for engineering thermoplastic composites. These desirable properties stem from the fact that macrocyclic polyester oligomers exhibit low melt viscosity, allowing them to impregnate a dense fibrous preform easily. Furthermore, certain macrocyclic polyester oligomers melt and polymerize at temperatures well below the melting point of the resulting polymer. Upon melting and in the presence of an appropriate catalyst, polymerization and crystallization can occur virtually isothermally. As a result, the time and expense required to thermally cycle a tool is favorably reduced.
Development of processing equipment for use with macrocyclic polyester oligomers has been limited. It is generally believed that production of molded parts from macrocyclic polyester oligomers requires existing equipment to be modified to allow for transfer of the macrocyclic polyester oligomers and polymerization catalysts into the equipment in the appropriate amounts at the appropriate time and at the appropriate temperature. Modifying existing equipment takes time and is often costly, and hence limits the application of macrocyclic polyester oligomers.
A blend of a macrocyclic polyester oligomer and a polymerization catalyst as a one component ready-to-use material with a long shelf life enables production of parts from macrocyclic polyester oligomers without the modification of existing equipment, thereby reducing time and cost of manufacture while expanding the application of macrocyclic polyester oligomers. In this blend material, the macrocyclic polyester oligomer remains intact in solid state at ambient conditions. Upon melting, the blend material initially forms a low viscosity fluid, and then rapidly polymerizes to form high molecular weight polyesters which subsequently solidify to form semi-crystalline polymers. In the case of certain macrocyclic polyester oligomers, for example, poly(1,4-butylene terephthalate), demolding can take place at the polymerization temperature, e.g., at about 180xc2x0 C. to 200xc2x0 C., because the resulting polyester polymer solidifies fairly rapidly at that temperature without cooling.
In one aspect, the invention generally features a blend material that includes a macrocyclic polyester oligomer, a polymerization catalyst, and optionally, a filler. In one embodiment, the macrocyclic polyester oligomer is substantially a homo- or co-polyester oligomer. Polymerization catalysts include, among others, tin compounds and titanate compounds.
In another aspect, the invention generally features a process for preparing a blend material as described above.
In yet another aspect, the invention features processes such as rotational molding, resin film infusion, pultrusion, resin transfer molding, filament winding, making and using powder coated or hot melt prepreg, compression molding, and roll wrapping, which use the blend material described above. These processes of the invention may be used to form polyester polymer composites which may be included in articles of manufacture such as carbon fiber golf shafts or lightweight automotive chassis members.
The foregoing and other objects, aspects, features, and advantages of the invention will become more apparent from the following figures, description, and claims.